1. Field of the Invention
The present invention relates to a glow plug with a pressure sensor used for an internal combustion engine or the like.
2. Description of the Related Art
Conventionally, a glow plug used, e.g., for assisting startup of an internal combustion engine such as a diesel engine, includes a tubular metallic shell which has an axial hole extending in an axial direction; and a heater member inserted into the axial hole; a center rod which is inserted into the axial hole and through which electric current is supplied to the heater member; etc. (see, for example, Patent Document 1). In some cases, a heater including a heating element which is disposed within a metallic tube and generates heat upon supply of electric current from the center rod is employed as the heater member.
Further, in recent years, a glow plug with a pressure sensor has been proposed which imparts a function of detecting pressure (e.g., combustion pressure). In such a glow plug with a pressure sensor, a heater member whose forward end portion projects from the forward end of a metallic shell is attached to the metallic shell via a deformable member which is deformable along the axis such that the heater member can move relative to the metallic shell. When combustion pressure is applied to move the heater member and the deformable member relative to the metallic shell, this relative displacement (movement) is transferred to the pressure sensor, which outputs a signal corresponding to the amount of relative displacement of the heater member (i.e., the pressure applied to the heater member and the deformable member).
In order for the deformable member to smoothly respond to combustion pressure or the like, an annular clearance is formed between the outer circumferential surface of the heater member (tube) and the inner circumferential surface of the metallic shell. More particularly, the annular clearance is formed in a region located on the forward end side of a junction portion of the deformable member which is joined to the heater member.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2009-520941
3. Problems to be Solved by the Invention
Soot produced as a result of operation of an internal combustion engine or the like may enter and clog the above-described clearance. In such a case, since the deformable member is hindered from receiving the full impact of the combustion pressure or the like, the resulting pressure detection sensitivity may be lowered.